Delegates in Cancún cheered deliriously as the agreement was passed, but as the negotiators from 193 nations returned home, the scale of the tasks ahead became clear, from deep cuts in carbon emissions to raising billions of dollars of climate aid. "We can step forward in South Africa if we can continue to consolidate and carry on the spirit of unity and co-ordination formed in the Cancún conference," said Xie Zhenhua, head of China's delegation. "But the negotiations in the future will continue to be difficult." Connie Hedegaard, the EU commissioner on climate action, agreed: "There is a very heavy work programme in the next year."

Patricia Espinosa, the Mexican foreign minister who presided over the talks, said the result was "the best we could achieve at this point in a long process". She was praised for her firm but inclusive chairing of the meeting, a critical missing factor in Copenhagen, leading the Indian environment minister to compare her to a goddess. "A global deal on climate change is now back on track," said Chris Huhne, the UK's climate change secretary.

The Cancún agreement (PDF) sets out a process towards the global, legally binding deal many observers believe will be essential to avoid the worst impacts of global warming. For the first time, it commits both rich and developing nations to curbing greenhouse gas emissions and sets up a Green Climate Fund to deliver financial aid to poorer nations bearing the brunt of climate change. It sets out in principle deals on tackling deforestation and providing wind turbines, solar panels and other low-carbon technology to developing nations. But the meeting in Durban next year will need to close the gap between the emission cuts offered to date and the much deeper cuts scientists say are needed if the UN's goal of keeping a temperature rise to under 2C is to be reached. Researchers from the Climate Action Tracker project said existing pledges set the world on course for 3.2C of warming.

The most daunting task ahead appears to be resolving the fate of the Kyoto protocol, for which Durban will be the last-chance saloon. The protocol is the only existing legally binding treaty, but it expires in 2012. However, some powerful nations want to see it killed, as it requires emissions cuts from only 37 of the richest industrialised nations. Japan caused a diplomatic upset in Cancún by declaring it would block a second phase for Kyoto, and was backed by Russia and Canada. Further complicating the issue is that the US never ratified Kyoto so, like China, the world's other super-polluter, it is not bound by it. Negotiators in Cancún parked the problem: those in Durban will not have that option.

The Cancún agreements on money for adaptation to warming, deforestation and technology transfer all represent good intentions but their success will depend on the details decided in Durban. For example, the Green Climate Fund decision was to set up a "transitional committee" to design the fund, with no agreement on how the $30bn by 2012 or $100bn by 2020 previously promised will be raised. Another sticking point had been how pledged national cuts would be policed. Todd Stern, the US state department climate change envoy, said Cancún had given substance to the notion of an inspections regime: meaning all the difficult details remain to be resolved.

After Copenhagen, Cancún had been billed as a test of multilateralism. "Cancún has done its job," said Christiana Figueres, head of the UN's climate treaty under which the talks take place. "Nations have shown they can work together under a common roof, to reach consensus on a common cause."

The dissenting voices that crashed Copenhagen dwindled in Cancún to just one – Bolivia – following intense diplomatic pressure. The Bolivian delegation's leader, Pablo Solón, denounced the Cancún deal as ignoring scientific reality: "Its cost will be measured in human lives."

Next year the Durban summit will have to turn Cancún's compromise into a real action plan. But some senior observers have suggested progress in combating climate change depends as much – or more – on action outside the UN process in the next year, with nations and regions making their commitments.